gmx dipoles -quad does not report quadrupole moment
Refactoring in 2009 broke this option: 1dfe3763 by inadvertently replacing Qlsq
with mulsq
Returning C-style output parameters (which was necessary at the time) made this bug easier to make. Returning the parameters as an output struct (or tuple) made it very clear that the input was the same for each dimension when computing the quadrupole components to report.